Various olefin fibers, i.e., fibers in which the fiber-forming substance is any long-chain, synthetic polymer of at least 85 weight percent ethylene, propylene, or other olefin units, are known from the prior art. The mechanical properties of such fibers are generally related in large part to the morphology of the polymer, especially molecular orientation and crystallinity. Thus, crystalline polypropylene fibers and filaments are items of commerce and have been used in making products such as ropes, non-woven fabrics, and woven fabrics. Polypropylene is known to exist as atactic (largely amorphous), syndiotactic (largely crystalline), and isotactic (also largely crystalline). The largely crystalline types of polypropylene (PP), including both isotactic and syndiotactic, have found wide acceptance in certain applications in the form of fibers.
Other types of polyolefins which have been suitably formed into fibers include high density polyethylene (HDPE), and linear low density polyethylene (LLDPE). These polymers are prepared using coordination catalysts and are generally known as linear polymers because of the substantial absence of branched chains of polymerized monomer pendant from the main polymer backbone. LLDPE is a linear ethylene polymer wherein ethylene has been polymerized along with minor amounts of .alpha.,.beta.-ethylenically unsaturated alkenes having from three to twelve carbon atoms per alkene molecule, and more typically four to eight. Although LLDPE contains short chain branching due to the pendant side groups introduced by the alkene comonomer and exhibits characteristics of low density polyethylene such as toughness and low modulus, it generally retains much of the strength, crystallinity, and extensability normally found in HDPE homopolymers. In contrast, polyethylene prepared with the use of a free radical initiator, such as peroxide, gives rise to highly branched polyethylenes known as low density polyethylene (LDPE) and sometimes as high pressure polyethylene (HPPE) and ICI-type polyethylenes. Because of unsuitable morphology, notably long chain branching and concomitant high melt elasticity, LDPE is difficult to form into a fiber and has inferior properties as compared to LLDPE, HDPE and PP fibers.
One application of certain fibers such as, for example, polyvinyl chloride, low melting polyester and polyvinylacetate, has been the use of such fibers as binder fibers by blending the binder fiber with high tenacity performance fibers such as polyesters, polyamides, cotton, wool or the like, and heating the fibrous mixture to near the melting point of the binder fiber to thermally weld the binder fiber to the performance fiber. This procedure has found particular application in non-woven fabrics prepared from performance fibers which would otherwise tend to separate easily in the fabric. However, because of the unavailability of reactive sites in the olefin fibers, the bonding of olefin fibers to the performance fibers is characterized by encapsulation of the performance fiber by the melted olefin fiber at the thermal welding site by the formation of microglobules or beads of the olefin fiber. Moreover, it is difficult to achieve suitable thermal welding in this fashion because of the poor wettability of a polar performance fiber by a nonpolar olefin fiber.
Another problem which has hampered the acceptance of olefin fibers is a lack of dyeability. Olefin fibers are inherently difficult to dye, because there are no sites for the specific attraction of dye molecules, i.e., there are no hydrogen bonding or ionic groups, and dyeing can only take place by virtue of weak van der Waals forces. Usually, such fibers are colored by adding pigments to the polyolefin melt before extrusion, and much effort has gone into pigmentation technology for dispersing a dye into the polyolefin fiber. This has largely been unsuccessful because of the poor lightfastness, poor fastness to dry cleaning, generally low color build-up, inflexibility, a necessity for continuous production changes, and the involvement of large inventories. As an alternative, some PP fibers have been modified, for example, with nickel and vinylpyridine.
Olefin fibers are typically fabricated commercially by melt spinning. In this procedure, the molten polymer is expelled through a die, e.g. a spinnerette, with subsequent drawing of the molten extrudate, solidification of the extrudate by heat transfer to a surrounding fluid medium, and taking up of the solid extrudate. Melt spinning may also include cold drawing, heat treating and/or texturizing. An important aspect of melt spinning is the orientation of the polymer molecules by drawing the polymer in the molten state as it leaves the spinnerette. Polyolefins which are not at least partially oriented by melt drawing generally lack suitable mechanical properties and are difficult to further orient by additional drawing of the solid filament. In order to optimize manufacturing processes, it is desirable to spin the fiber at high speeds. In accordance with standard terminology of the fiber and filament industry, the following definitions apply to the terms used herein:
A "monofilament" (also known as "monofil") refers to an individual strand of denier greater than 15, usually greater than 30;
A "fine denier fiber or filament" refers to a strand of denier less than 15;
A "multi-filament" (or "multifil") refers to simultaneously formed fine denier filaments spun in a bundle of fibers, generally containing at least 3, preferably at least 15-100 fibers and can be several hundred or several thousand;
"Staple fibers" refer to fine denier strands which have been formed at, or cut to, staple lengths of generally one to eight inches (2.5 to 20 cm);
An "extruded strand" refers to an extrudate formed by passing polymer through a forming-orifice, such as a die;
A "fibril" refers to a super fine discrete filament embedded in a more or less continuous matrix;
A "biconstituent fiber" refers to a fiber comprising two polymer components in continuous and/or dispersed phases;
A "bicomponent fiber" refers to a fiber comprising two polymer components, each in a continuous phase, e.g. side by side or sheath/core.
Convenient references relating to fibers and filaments, including those of man-made thermoplastics, and incorporated herein by reference, are, for example:
(a) Encyclopedia of Polymer Science and Technology, Interscience, New York, vol. 6 (1967), pp. 505-555 and vol. 9 (1968), pp. 403-440;
(b) Kirk-Othmer Encyclopedia of Chemical Technology, vol. 16 for "Olefin Fibers", John Wiley and Sons, New York, 1981, 3rd edition;
(c) Man Made and Fiber and Textile Dictionary, Celanese Corporation;
(d) Fundamentals of Fibre Formation--The Science of Fibre Spinning and Drawing, Adrezij Ziabicki, John Wiley and Sons, London/New York, 1976;
(e) Man Made Fibres, by R. W. Moncrieff, John Wiley and Sons, London/New York, 1975.
Other references relevant to this disclosure include U.S. Pat. No. 4,644,045 which describes spun bonded non-woven webs of LLDPE having a critical combination of percent crystallinity, cone die melt flow, die swell, relation of die swell to melt-index, and polymer uniformity; European patent application no. 85101380.5 which describes fine denier fibers and/or multi-filaments of LLDPE; and European patent application no. 87304728.6 which describes a non-woven fabric formed of heat bonded bicomponent filaments having a sheath of LLDPE and a core of polyethylene terephthalate.
In CA 91:22388p (1979) there is described a fiber comprising polypropylene and ethylene-maleic anhydride graft copolymer spun at a 50:50 ratio and drawn 300% at 100.degree. C., and a blend of the drawn fibers and rayon at a 40:60 wt. ratio carded and heated at 145.degree. C. to give a bulky non-woven fabric. However, polypropylene is disadvantageous in some applications because of its relatively high melting point (145.degree. C.), and because of the relatively poor hand or feel imparted to fabrics made thereof. Poor hand is manifested in a relatively rough and inflexible fabric, as opposed to a smooth and flexible fabric.
U.S. Pat. No. 4,684,576 describes the use of blends of HDPE grafted with maleic acid or maleic anhydride to give rise to succinic acid or succinic anhydride groups along the polymer chain with other olefin polymers as an adhesive, for example, in extrusion coating of articles, as adhesive layers in films and packaging, as hot melt coatings, as wire and cable interlayers, and in other similar applications. Similar references describing adhesive blends containing HDPE grafted with unsaturated carboxylic acids, primarily for laminate structures, include U.S. Pat. Nos. 4,460,632; 4,394,485; and 4,230,830; and U.K. patent application nos. 2,081,723 and 2,113,696.